1. Field of the Invention
The present invention relates to a fluorine-containing elastomer composition prepared using perfluoroelastomers having different contents of a perfluoro(alkyl vinyl ether) unit, and a sealing material made of the composition. The present invention also relates to curable compositions and the molded articles of perfluoroelastomers (FFKM) having excellent thermal and plasma resistance.
2. Description of Related Art
Fluorine-containing elastomers, particularly perfluoroelastomers mainly comprising tetrafluoroethylene (TFE) unit exhibit excellent chemical resistance, solvent resistance and heat resistance, and therefore are widely used for a sealing material, etc. used under strict environments.
However with advances in technologies, the characteristics required have been made more rigorous, and in the fields of aeronautics, space industries, semiconductor manufacturing equipment and chemical plant, sealing property under a high temperature environment of not less than 300° C. is demanded.
Accordingly, for improving the curing speed, Japanese Patent Document JP2001-504885A discloses a curable composition prepared by adding a curing accelerator such as an organic or inorganic ammonium salt to a mixture of a perfluoro elastomer and a curing agent.
Perfluoroelastomeric materials are known for their chemical resistance, plasma resistance, and when used in compositions having typical filler or reinforcing systems for acceptable compression set resistance levels and mechanical properties. As such, they have been applied for many uses, including for use as elastomeric sealing materials in applications where a seal or gasket will be subject to highly corrosive chemicals and/or extreme operating conditions, and for use in forming molded parts that are capable of withstanding deformation. FFKMs are also well known for use in the semiconductor manufacturing industry as sealing materials due to their chemical and plasma resistance. Such materials are typically prepared from perfluorinated monomers, including at least one perfluorinated cure site monomer. The monomers are polymerized to form a perfluorinated polymer having the cure sites from the cure site monomer(s) and then cured (cross-linked) to form an elastomer. Typical FFKM compositions include a polymerized perfluoropolymer as noted above, a curing agent that reacts with the reactive cure site group on the cure site monomer, and any desired fillers. The cured perfluoroelastomer exhibits typical elastomeric characteristics.
FFKMs are generally known for use as O-rings and related sealing parts for high-end sealing applications due to their high purity, excellent resistance to heat, plasma, chemicals and other harsh environments. Industries that require their use in such environments include semiconductor, aerospace, chemical and pharmaceutical. The development of new perfluoroelastomer compositions using these materials faces ever-increasing demands and challenges for FFKMs and compositions based on FFKMs that have the ability to provide greater thermal, chemical and plasma resistance. Industry demands, particularly in the semiconductor area continue to require enhanced performance of such seals to meet new end-use applications that have increasingly aggressive environments as well as lower and lower contamination and particulation requirements.
As is recognized in the art, different FFKM compositions may include different curatives (curing agents) depending on the type of cure site monomer (CSM) structure and corresponding curing chemistry. Such compositions may also include a variety of fillers and combinations of fillers to achieve target mechanical properties, compression set or improved chemical and plasma resistance. For semiconductor sealing applications, both inorganic and organic fillers can be used to improve plasma resistance depending on the type of plasma chemistry. Typical fillers include carbon black, silica, alumina, fluoroplastics, barium sulfate and other plastics. Fillers used in some FFKM compositions for semiconductor applications include fluoroplastic filler particles formed of polytetrafluoroethylene (PTFE) or melt-processible perfluorinated copolymers such as copolymers of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) (also referred to as FEP-type copolymers) or of TFE and perfluoroalkylvinyl ethers (PAVEs) (known as PFA-type copolymers), particularly in nanomer-sized particles.
U.S. Pat. No. 6,710,132 discloses a blend of an FFKM with semi-crystalline fluoroplastic particles (such as PTFE), wherein the particles have a core-shell structure and are formed by latex blending of these materials.
U.S. Pat. No. 4,713,418 discloses a composition formed by melt blending an FFKM and a melt-processible thermoplastic fluoropolymer. The patent asserts that particles of about 10 microns are reformed from some of the melted thermoplastic upon recrystallization. U.S. Patent Publication No. 2005/0261431 A1 discloses melt blending an FFKM and a semicrystalline polymer such as PTFE and/or a copolymer, such as the PFA-type copolymer, of greater than an average size of 100 nm wherein blending temperature or curing temperature exceeds the melting temperature of the fluoroplastic fillers.
U.S. Pat. No. 7,019,083 and International Publication WO2006/120882 A1 disclose crosslinkable fluoroplastics.
When an FFKM composition includes a semicrystalline fluoroplastic particle filler, such as microparticles or nanoparticles of PTFE or copolymers such as those of the PFA-type, good physical properties, good plasma resistance and excellent purity are achieved. For semiconductor applications, such systems also help to avoid metallic particulation and contamination at a level improved over FFKMs, which have inorganic fillers such as metal oxides. However, there is a need in the art to develop more simplified processing methods to form fluoropolymer-filled FFKMs. Latex blending can be expensive for large-scale, commercial batches and melt blending generally requires temperatures of up to 350° C. Filler loading in many commercial products is generally limited to up to about 30 weight percent of the base polymer. Due to the use of the fluoropolymeric fillers, such compositions can also sometimes have a relatively high compression set especially at high temperatures (e.g., >300° C.). Moldability and bondability can also be limited due to use of such fluoropolymeric fillers.
There is a need in the art for further improvements to perfluoroelastomer compositions which, upon cure, provide high thermal resistance, low compression set, good plasma resistance, relatively low hardness, sufficient strength and elongation which meet the increasingly demanding requirements for use in high-end sealing applications like those of semiconductor processing.